Two complementary approaches for the direct synthesis of 2-dichloro- and 2-trichlorobenzoxazoles from 2-aminophenols and halogenated nitriles are reported. A green, noncatalyzed method was shown to proceed in an alcoholic solvent without the addition of exogenous acid or base. This method provides a clean and robust synthesis of these important heterocycles, which contain a key functional group handle at the 2-position. A complementary platinum multifaceted catalysis approach was also developed in which the metal can catalyzes multiple mechanistically distinct processes. This method allows for an improved use of the metal catalyst vs stepwise protocols and provides increased flexibility in the choice of reaction conditions.Keywords: Alcoholic solvent; Green chemistry; Heterocycle; Multifaceted catalysis; Platinum catalysis

A mild platinum-catalysed method for the formation of free amidines from the reaction of amines and trichloroacetonitrile in nonpolar solvents has been developed. This protocol provides access to novel amidines that in some cases (4b–d) cannot be synthesised via the direct reaction of amines and halogenated nitriles.

A novel gold-catalyzed method for the regioselective synthesis of highly substituted pyrroles directly from oximes and alkynes was developed via independent optimization of two key steps of the process. Importantly, a cationic gold(I) species was shown to activate multiple steps along the reaction pathway and therefore act as a multifaceted catalyst. Initial gold-promoted addition of the oxime oxygen to the activated alkyne afforded the O-vinyloxime in situ. The O-vinyloxime was subsequently transformed into the pyrrole via a gold-catalyzed tautomerization, [3,3]-sigmatropic rearrangement, and cyclodehydration process. Notably, this method provides a functional group handle in the form of an ester at the 3/4-position for further exploitation. The proposed mechanistic pathway is supported by a novel application of the Huisgen cycloaddition click reaction, which was used to probe the relative stability of substituted O-vinyloximes. The intermediacy of N-alkenylhydroxylamine O-vinyl ethers and imino ketones or imino aldehydes along the reaction pathway were determined by high-temperature 1H, 2H{1H}, and 13C{1H} NMR experiments. X-ray crystallographic evidence was used to further support the mechanistic hypothesis.

O-Vinyl oximes were synthesised from the reaction of oximes with activated alkynes and subsequently rearranged using gold catalysis to afford highly substituted pyrroles in an efficient and regiocontrolled process. Additionally, pyrroles were formed directly from oximes and activated alkynes in a multifaceted catalysis process.

A step-economical one-pot nucleophilic catalysis/thermal Claisen-rearrangement protocol for the direct synthesis of α-formyl-α-allylacetates from allylic alcohols and activated alkynes has been developed. The product α-formyl-α-allylacetates were further reacted in situ to give either protected enol ethers or β-hydroxy-4-pentenoates.

O-Vinyl oximes were synthesised from the reaction of oximes with activated alkynes and subsequently rearranged using gold catalysis to afford highly substituted pyrroles in an efficient and regiocontrolled process. Additionally, pyrroles were formed directly from oximes and activated alkynes in a multifaceted catalysis process.